Well it's confirmed by Nick Renqvist, a 3DMark developer.
First of all (and this shouldn't come as a shocker to anyone) the next generation 3DMark will be Windows Vista only, and will require DX10 compliant hardware. You may ask: Why no fallback to DX9 then? Well, we already have a Vista enabled DX9 benchmark (3DMark06) and the last three 3DMarks have all been DX9; 3DMark03 has one test which requires SM2.0, 3DMark05 requires SM2.0 for all tests and 3DMark06 uppers the requirements for two tests to SM3.0. I think both we and the rest of the world are ready to step into the next generation - DX10. There's no reason to go backwards, if you know what I mean.